Telephone substation circuits



Oct. 30, 1928.

Filed Oct. 23, 1925 3 Sheets-Sheet 1 Imrs Harold L. P e

Qct. 30,

H. C. PYE

TELEPHONE SUBSTATION CIRCUITS Filed Oct. 25, 1925 3 Sheets-Sheet 3 Oct. 30, 1928. 1,689,598

H. c. PYE

TELEPHONE SUBSTATION CIRCUITS Filed Oct. 25, 1925 5 Sheets-511a 3 Patented Oct. 30, 1928.

UNITED STATES PATENT OFFICE.

HAROLD C. PYE, OF OAK PARK, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

TELEPHONE SUBSTATION CIRCUITS Application filed October 23, 1925. Serial No. 64,293.

This invention relates in general to telephone substation circuits, but more especially to substation circuits for automatic telephone systems; and the principal object of the invention is to provide a new and improved common battery anti side tone circuit for an automatic telephone.

A further object of this invention is to provide an anti side tone substation circuit equipped with a calling device to permit its use in an automatic telephone system.

A further object of this invention is to provide a new and improved telephone substation circuit in which are combined the advantages of the well known booster type circuit and the common battery anti side tone circuit.

A further object of this invention is to provide an anti side tone booster telephone circuit in which the amount of equipment required is reduced to a minimum without impairing the efficiency of the substation either during the sending or reception of telephone signals. it

A still further object of the invention is to provide a substation circuit of the class described adaptable for use in a cradle type telephone and using a three conductor cord to connect the monophone to the desk stand.

A still further object of the invention is to provide a substation circuit of the class described adaptable to employ either a permanent magnet receiver or a direct current receiver.

A further object is to provide an automatic substation circuit in which the transmitter is shunted by a high resistance path through which direct current wili flow to maintain theestablished connection if the transmitter opens its circuit.

Further objects not specifically mentioned here will be apparent from the detailed description and claims which follow.

The drawings comprisin Figs. 1 to 9, in elusive, show the details o my invention in three different forms. Figure 1 shows the invention adapted to use a direct current receiver in an automatic anti side tone telephone substation, this form of substation requiring a four conductor cord comprising conductors (J extending between the bell box and telephone. Figure 4 shows a. modification of the circuit of Figure 1, the modification permitting the reduction of the number of cord conductors from four to three. In Fig. 7, I show a substation circuit built in accordance with the objects of this invention and employing a permanent manget receiver instead of the direct current receiver as employed in the other figures. Figures 2 and 3 are respectively the talking circuit and dialling circuit of the substation shown in Fig. 1, while Figs. 5 and 6 are respectively the talkng and dialling circuits of the substation shown in Fig. 4, and Fi s. 8 and 9 are respectively the talking and dialling circuits of the substation shown in Fig. 7. Referring now particularly to Fg. 1, it will be noted that the substation comprises the usual ringer 1O bridged across the line conductors 1 and 2 in series with the condenser 9; and that the circuit through the calling device impulse spring 3 the hook switch springs 5, the transmitter 7, induction coil winding 13, and the direct current receiver 8, is normally held open by the hook switch springs 5 and 6. The secondary winding 14 of the induction coil is inductively coupled to the primary 3 and placed in multiple with the transmitter T in series with the condenser 9 as is the usual practice in booster telephone circuits in addition to this standard substation equipmcnt, I have provided a third winding in the induction coil, that winding 12, being a relatively large number of turns of fine wire forming a relatively high resistance winding which together with the additional condenser 11 forms a balancing circuit, that circuit being commonly referred to as the artificial line. During impulsing, the manipulation of the calling device operates the shunt springs 4 to short circuit the transmitter and receiver in accordance with the well established practice, the impulse springs 3, operating to open the circuit through the substation connecting the conductors 1 and 2 to operate the automatic switching equipment at the exchangc to set up the call in the well known manner. From Fig. 3, it will be noted that during the impulsing the windings 12 and 13 of the induction coil are short circuited, and that the winding 14 in parallel with the ringer 10, is bridged across the impulse spring 3 in series with the condenser 9, forming the equivalent oi the iln ulsing circuit shown in the application of Martin, Serial No. 452,467 and filed March 15, 1921.

Referring now to Fig. 2, which shows the talking circuit of the substation simplified as much as possible to enable a clear understanding of the operation, it will be remembered that the condition to be met in a per fect anti side tone substation circuit are a balance for receiving and a balance for transmitting. During transmission when the transmitter is considered a source of E. M. F., the substation circuits must be balanced so that no current flows through the receiver, and during receiving when the line is the source of the E. M. F., the substation circuit must be balanced so that no current flows through the artificial line circuit. Commercially this condition is impossible because the balancing circuit would have to be different for each line on which the substation was used, and would be different for each frequency of current sent through the substation. The well designed commercial anti side tone telephone circuit approximates these conditions as nearly as possible, reducing the current flow through the receiver during transmission to such a point as to leave only an unobjectionable receiver response, that response being too weak to be noted. During receiving a small current flow through the artificial line, its amount being so small asnot to materially decrease the elficiency of the substation.

Considering the action of the substation during sending, it will be noted in Fig. 1 that the direct current from the battery feed at the central office passes over the line conductor 1 through the transmitter 7, through the winding 13 of the induction coil, through the direct current receiver 8, through the line conductor 2 and thence back to the central office. The condensers 9 and 11 prevent the flow of any direct current through the windings 14 and 12 of the induction coil, respectively. The action of the voice on the transmitter 7 causes it to vary this direct current changing it into an undulating current, which upon flowing through the winding of 13 of the induction coil, induces in the windings 13 and 14 an alternating current of proportional strength. This autotransformer action of the windings 13 and 14 am lifies the variations in current strength pro need in the line by the transmitter, the combined alternating and undulating current flowing over two paths, the one through the condenser 9 over the conductor 1, through the external line circuit to the conductor 2 and the other through the artificial line circuit comprising winding 12 of the induction coil and the condenser 11 in series. If the substation circuit is in erfect balance the impedance drop of t ese two circuits will be exactly equal and therefore the two ends of the receiver 8 will be at the same potential and no current willflow through it, and the speech picked up by the transmitter 7 will not be reproduced by the receiver 8. It will be noted that the auto transformer windings 13 and 14 are directly shunted by the ringer 10, but inasmuch as the ringer is of very high impedance, onlg a very small current flows through this pat and its efi'ect is practically negligible.

During the time that the substation is receiving signals an E. M. F. will be present across the line conductors 1 and 2, this E. M. F. being alternating and pro ortional to the strength of the signal that is eing received. The current flowing in over the conductor 2, tends to divide into two paths, the one through the artificial line circuit comprising condenser 11 and the winding 12 of the induction coil, and the other path including the receiver 8, the windings 13 and 14 of the induction coil, the condenser 9 and the line conductor 1 and thence back into the external line circuits. The current flowing through the windings 13 and 14 of the induction coil induces in the Winding 12 an electro-motive force in such a direction as to oppose the flow of current through the artificial line. The transmitter 7 being in parallel with the condenser 9 and the winding 14 of the induction coil afio-rds a parallel path for some of the alternating current during receiving. However, this arrangement is identical to that of the side tone booster circuit, and while it introduces a certain loss, it is unavoidable and not particularly serious.

As in transmitting the ringer 10 and the condenser 9 are bridged across the line conductors 1 and 2, but the impedance of the ringer is so high that the alternating current flowing through this branch is negligible in amount and effect.

The substation shown in Fig. 4 is a modification of that just explained, the modifications being such as to permit the use of a three conductor cord instead of a four conductor cord. This modification is particularly adaptable when the circuit is used in a cradle type telephone, the three conductor cord comprising conductors C being used between the hand telephone and the desk stand. Because of the similarity of the circuit shown in Fig. 4 and that shown in Fig. 1, the corresponding parts are the same reference numerals in the two figures. By comparing the talking circuit shown in Fig. 5 with that shown 1n Fig. 2, it will be noted that the modification Consists essentially in reversin the order of the windings 13 and 14 and t ie condenser 11 with respect to the line conductors 1 and 2, and in connecting the transmitter from the receiver to the junction of windings 13 and 14 and in bridging the ringer across the three windings 12, 13. and 14 of the induction coil instead of one of the two windings as before. The main direct current path now consists of conductor 1, winding 13, transmitter 7 receiver 8 to conill ductor 2 and thence over the external circuit to the battery feed at the exchange. In addition, there is an auxiliary direct current path from conductor 1, through ringer 10, winding 12, receiver 8 to conductor 2. This auxiliary path having utility in that it holds the substation circuits closed to direct current even though the transmitter momentarily opens. The resistance of ringer 10 is sufficiently low to hold the battery feed relays at the exchange in an energized position. The undulations in this direct current set up in the winding 13 by the variations caused by the transmitter 7, induce an alternating current in the windings l3 and 14, which flows over two circuits, the one over line conductor 1 through the external circuit to line conductor 2 to the receiver 8, condenser 11, coils 14 and 13, and the other to the winding 12 of the induction coil, the condenser 9, to the line circuit 2 thence over the external line circuit 1, to the windings 13 and 14 and condenser 11. As before, if the artificial line is equivalent to the external circuit the two ends of the receiver 8 will be at the same potential and no current will flow through it. Upon reception the alternating E. M. F. impressed on the line conductors 1 and 2 tends to drive the current over two parallel paths, the one to the artificial line comprising conductors 9 and 12, induction coil winding 12, thence through condenser 11, windings 14 and 13 to the line conductor 1, and the ,second path through the receiver 8, thence through the condenser 11 and the windings 14 and 13 to the conductor 1, and the second path through the receiver 8, thence through the condenser 11 and the windings 14 and 13 to the conductor 1. As before, the voltage induced in the winding 12 by the current flowing through the windings 14 and 13 opposes the flow of current through the artificial line included in 9 and 12. The ringer which is bridged directly across the windings 12, condenser 11 and windings 14 and 13 does not materially efl'ect the action of the circuit, except to "guard against the possibility of premature release of the established connection in case the transmitter opens its circuit.

The substation circuit that I have shown in Figs. 1 and 4 employ a receiver of the direct current type. Direct current receivers, while quite satisfactory in operation of relatively short lines, are not as sensitive as the permanent magnet type receiver, and it is therefore desirable that an anti side tone circuit employsa permanent magnet receiver, particularly if that telephone is to be used on a relatively lon line. Accordingly I have modified the circuit of the substation in my invention in a manner shown in Fig. 7, to adapt it to use a permanent magnet type of receiver. In the cireuit using the direct current receiver, the transmitter B current was sent directly to the receiver, serving to polarize it. Permanent magnet receivers, however, are not adapted to handle sufiicient direct current, and the circuit must be changed so that the transmitter feed does not come through the receiver circuit. Anti side tone substation circuits employing a permanent magnet receiver have in the past brought transmitter current through the artificial line, the resistance of which is sufliciently high to seriously impair the eificienc of the transmitter. In fact in some anti side tone circuits :1 special low current transmitter must be used in order that the substation will operate satisfactorily.

Referring now to the talking circuit shown in Fig. 8, it will be seen that I have arranged the substation circuits so that the transmitter feed current traverses neither the receiver circuit or the artificial line circuit, but rather upon entering the substation over conductor 32 flows through only the low resistance winding 43 of the induction coil and the transmitter 47 and pass out over the conductor 31. The direct current flowing over this circuit is varied by the transmitter causing an undulating current to flow through the winding 43 of the induction coil, which induces an alternating current in the windings 43 and 42, that alternating current flowing over the circuit including conductor 32, windings 43 and 42, to the condenser 39 to the conductor 31 and thence over the external circuit, joining the undulating transmitter current to reenforce it in the manner of the well known booster circuit. Considering the transmitter as a source of E. M. F., current flows out to the junction point between the windings 42 and 43 of the induction coil and thence divide, part goin through the winding 43 and part through t e winding 42. Inasmuch as these two windings are in the same direction, with current flowing 'to them in opposite directions, and inasmuch as the current turn ratios of the two windings are equal the inductive effect upon the winding 44 is neutralized and the reeciver 48 remains inactive.

During reception of signals there is a source of alternating potential across the conductors 31 and 32 tending to drive a current through two paths in the substation, the one running from conductor 31 through the transmitter 47, through the winding 43 of the induction coil to the conductor 32, and the other from the conductor 31, through the condenser 39 and the winding 42 of the induction coil, through the winding 43 of the induction coil and thence to the condu'ctor 32. The current through the winding 43 induces a counter E. M. F. in the winding 42 which opposes the flow of current througn the artificial line circuit included in winding 42 and condenser 39. This current flowing in 43 induces a current to flow in winding 44 which actuates the receiver 48, causing it to reproduce the incoming signal.

Referring to the impulsing circuit shown in Fig. 9 it will be seen that during the impulsing the operation of shunt spring 34 short circuits the winding 44 of the induction coil and the transmitter so that the substation circuit provides an invariable path from conductor 31 to conductor 32 throughthe impulse spring 33 and the winding 43 of the induction coil. The windings 43 and 42 of the induction coil are connected in multiple with the ringer 40, that multiple combination being connected across the impulse springs 33 in series with the condenser 39, an arrangement identical to that of the above mentioned Ma'rtin patent.

Thus it will be seen that I have devised new and useful substation telephone circuits of the anti side tone variety which employ a minimum of additional equipment and which employs the equipment involved in such a manner as to operate it efficiently.

Having thus described my invention what I consider new and desire to have protected by Letters Patent is pointed out in the appended claims.

What is claimed is:

1. In an automatic telephone substation, a group of equipment comprising a ringer, a condenser and an induction coil, a second group comprising a transmitter and a receiver, and circuit means for connecting said elements to form a common battery booster anti side tone circuit, said means including a cord ofonly three conductors connected between said equipment groups.

2. In an automatic telephone substation, a group of equipment comprising a ringer, a calling device, a condenser, and an induction coil, a second group of equipment comprisiug a transmitter and a receiver, a three conductor cord connecting said groups together, a line circuit, impulse springs in said calling device arranged to alternately open and close said line circuit, spark quenching means for said impulse springs comprising said ringer and a condenser bridged across said line circuit, a low inductance shunt for said ringer comprising windings of said induction coil, and means comprising a third winding of said induction coil for reducing the inductance of said shunt path to reduce the condenser current through said ringer thereby preventing its tapping during impulsing.

3. In an automatic telephone substation, a calling device comprising impulse springs and shunt springs, a transmitter, a receiver, a ringer and a condenser, an induction coil, a line circuit across which are bridged said condenser and ringer, a second bridge across said line circuit including said impulse springs, transmitter and one winding of said induction coil, a second winding of said induction coil connected from the junction of said transmitter and first winding to the junction of said condenser and ringer, said first and second windings jointly shunting said ringer, a circuit for said receiver including a third winding of said induction coil, circuits controlled by said shunt springs for short circuiting said transmitter and receiver during the transmission of impulses, spark protective means for said impulse springs comprising said condenser, ringer and shunt circuits, and means comprising said short circuited receiver and said third winding for reducing the inductance of said shunt circuit, thereby still further reducing the condenser discharge current through said ringer to prevent tapping of said ringer during impulsing.

4. In a telephone substation, a transmitter, an induction coil and a receiver, a line circuit, a calling device comprising impulse springs and shunt springs, a permanently closed bridge across said line circuit comprising a ringer and a condenser, a second, normally open bridge comprising one winding of said induction coil, said transmitter and said impulse springs, a second winding of said induction coil in multiple with said transmitter, a circuit for said receiver including a third windin of said induction coil, means including said shunt spring for short circuitin said transmitter and receiver during t e operation of said callin device, and circuit means for connecting sai elements together in a balanced circuit so that said receiver is unresponsive to current variations produced in said line by said transmitter.

5. In an automatic telephone substation, a calling device comprising impulse springs and shunt springs, a transmitter, a receiver, a ringer and a condenser, an induction coil, and a hook switch, a line circuit, a normally closed bridge across said line circuit includin said condenser and ringer, a second bridge including normally open contacts of said hook switch, said impulse s rings, transmitter and a winding of said in action coil, a circuit for said receiver including a second winding of said induction coil and a conductor in common with said second bridge, a shunt circuit for said ringer including a third winding of said induction coil, a set of normally open hook switch contacts and said first induction coil winding, and means including said shunt springs for short circuiting said receiver, transmitter and second induction coil winding to prevent sparking at said impulse springs.

6. In an automatic telephone substation in which a transmitter and receiver are formed as a unitary structure, an e uipment group comprising a calling device aving impulse springs and shunt springs, a rin er and condenser and a three winding in uction coil,

connecting means including a three conductor cord between said unitary structure and 5 apparatus group joining said units to form an automatic anti-side tone telephone substation, and circuit means controlled by said shunt springs for bridging said condenser and induction (oil windings around said impulse springs in a circuit excluding said three conductor cord to prevent sparking during the operation of said calling device.

7. In an automatic telephone substation, a transmitter, a receiver, a three winding induction coil, a condenser, a ringer. a calling device having impulse springs and shunt springs, a hook switch and a plurality of contacts controlled thereby, a line circuit. a permanently closed bridge across said line circuit comprising said ringer and con- CERTIFICATE OF Patent No. 1,689, 598.

denser, a second and normally open bridge across said circuit comprising certain of said hook switch contacts, said impulse springs, transmitter and one winding of said induction coil, a local circuit for said receiver including a second Winding of said induction coil and a conductor in common with said second bridge, said third winding being connected from the common point of said ringer and condenser through a contact set of said hook switch to said common conductor to form with said condenser a shunting means for said transmitter and impulse springs, and to form with said first winding, a shunt means for said ringer.

In witness whereof, I hereunto subscribe my name this 19th day of October, A. D., 1925.

HAROLD C. PYE.

CORRECTION.

Granted October 30, 1928, to

HAROLD C. PYE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

word "monophoue" read "hand telephone";

Page 1, line 29, for the and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of January, A. D. 1929.

(Seal) M. J. Moore, Acting Commissioner of Patents.

springs and shunt springs, a rin er and condenser and a three winding in uction coil,

connecting means including a three conductor cord between said unitary structure and 5 apparatus group joining said units to form an automatic anti-side tone telephone substation, and circuit means controlled by said shunt springs for bridging said condenser and induction (oil windings around said impulse springs in a circuit excluding said three conductor cord to prevent sparking during the operation of said calling device.

7. In an automatic telephone substation, a transmitter, a receiver, a three winding induction coil, a condenser, a ringer. a calling device having impulse springs and shunt springs, a hook switch and a plurality of contacts controlled thereby, a line circuit. a permanently closed bridge across said line circuit comprising said ringer and con- CERTIFICATE OF Patent No. 1,689, 598.

denser, a second and normally open bridge across said circuit comprising certain of said hook switch contacts, said impulse springs, transmitter and one winding of said induction coil, a local circuit for said receiver including a second Winding of said induction coil and a conductor in common with said second bridge, said third winding being connected from the common point of said ringer and condenser through a contact set of said hook switch to said common conductor to form with said condenser a shunting means for said transmitter and impulse springs, and to form with said first winding, a shunt means for said ringer.

In witness whereof, I hereunto subscribe my name this 19th day of October, A. D., 1925.

HAROLD C. PYE.

CORRECTION.

Granted October 30, 1928, to

HAROLD C. PYE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

word "monophoue" read "hand telephone";

Page 1, line 29, for the and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of January, A. D. 1929.

(Seal) M. J. Moore, Acting Commissioner of Patents. 

